Cell differentiation

[kfcman289]

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I had a Kaplan question where a certain ectoderm cell that was meant to be a feather in a chicken was put into a location where feet beaks, and the beak cell grew. The kaplan answers said it was because mesoderm cells induced the ectoderm cells.

Can someone explain what is going on whether or not ectoderm cells are already differentiated at the moment of gastrulation?

 

[DrknoSDN]

Tough question, I majored in molecular biology and human genetics and I think there is still a lot of research being done regarding cellular differentiation and determination.

I can say that the explanation provided is possible and has been demonstrated in various real experiments. When exactly determination actually occurs is not as well understood.
Once you get beyond the 8 cell stage and lose totipotency, differentiation is more of a gradient where most cells will be determined to a specific germ layer between X and Y cell count.
This is especially significant in the regions separating two zones, where concentrations of the cell-cell determinants may be different.

To answer for Kaplan, if that experiment was performed, and those were the results you got, it would be because the 'ectoderm' was induced to change.

On the MCAT I'd say the question and answer choices would play a big role in answering a question like this. This might simply be the "least wrong" of the options provided.

 

[inasensegone]

Tough question, I majored in molecular biology and human genetics and I think there is still a lot of research being done regarding cellular differentiation and determination.

I can say that the explanation provided is possible and has been demonstrated in various real experiments. When exactly determination actually occurs is not as well understood.
Once you get beyond the 8 cell stage and lose totipotency, differentiation is more of a gradient where most cells will be determined to a specific germ layer between X and Y cell count.
This is especially significant in the regions separating two zones, where concentrations of the cell-cell determinants may be different.

To answer for Kaplan, if that experiment was performed, and those were the results you got, it would be because the 'ectoderm' was induced to change.

On the MCAT I'd say the question and answer choices would play a big role in answering a question like this. This might simply be the "least wrong" of the options provided.

Solid explanation IMO... especially regarding the approach to this question on the MCAT.

 

[StIGMA]

The idea is that multiple tissue types form organs (ectoderm, mesoderm, endoderm), and the interactions between these tissues affect each other. The mesoderm cells at the location of the beak secrete factors / interact with the ectodermal cells. Most adult tissues have 'adult stem cells' or other undifferentiated cells that are not totipotent or even pluripotent (can form all 3 germ layers) but are oligo/multipotent. It is not necessary to know this to answer the question. In the question, they tell you that the tissue is not differentiated (it has not yet formed a feather). Instead, they place this undifferentiated cell in a different location where feathers do not form; rather, they place it where the beak is formed- and it becomes a beak. Why is this? The mesoderm (or tissue where you place it) interacted with it and altered its differentiation course (eg: in real terms, changed its signaling pathways/ gene expression signature).

The idea is that if you take an undifferentiated tissue/cell, even from an adult organism, and place it in another location, it can be in induced into a different differentiation track.

 

[kfcman289]

Ok, so just to clarify

Tough question, I majored in molecular biology and human genetics and I think there is still a lot of research being done regarding cellular differentiation and determination.

I can say that the explanation provided is possible and has been demonstrated in various real experiments. When exactly determination actually occurs is not as well understood.
Once you get beyond the 8 cell stage and lose totipotency, differentiation is more of a gradient where most cells will be determined to a specific germ layer between X and Y cell count.
This is especially significant in the regions separating two zones, where concentrations of the cell-cell determinants may be different.

To answer for Kaplan, if that experiment was performed, and those were the results you got, it would be because the 'ectoderm' was induced to change.

On the MCAT I'd say the question and answer choices would play a big role in answering a question like this. This might simply be the "least wrong" of the options provided.

Ok, so to clarify, past 8 cells, has indifferent cleavage stopped? Because I thought that the Morula has pretty much all identical cells?

 

[kfcman289]

The idea is that multiple tissue types form organs (ectoderm, mesoderm, endoderm), and the interactions between these tissues affect each other. The mesoderm cells at the location of the beak secrete factors / interact with the ectodermal cells. Most adult tissues have 'adult stem cells' or other undifferentiated cells that are not totipotent or even pluripotent (can form all 3 germ layers) but are oligo/multipotent. It is not necessary to know this to answer the question. In the question, they tell you that the tissue is not differentiated (it has not yet formed a feather). Instead, they place this undifferentiated cell in a different location where feathers do not form; rather, they place it where the beak is formed- and it becomes a beak. Why is this? The mesoderm (or tissue where you place it) interacted with it and altered its differentiation course (eg: in real terms, changed its signaling pathways/ gene expression signature).

The idea is that if you take an undifferentiated tissue/cell, even from an adult organism, and place it in another location, it can be in induced into a different differentiation track.

Ok, but both the beak and feather would be considered ectodermal cell. Is it possible to take an ectodermal cell and induce it to change into a mesodermal cell? Also, are mesodermal cells the only type of cells that can induce change in ectodermal cells?

 

[StIGMA]

It is possible to convert ectodermal cells to mesodermal cells in a lab but not in the context of this question. The cells are partially differentiated into ectoderm / mesoderm. They remain ectoderm / mesoderm. The not fully differentiated ectoderm can differentiate into ectodermal derivatives (feather or beak) depending on its tissue (organ) context.

To you last question, other ectodermal cells / endodermal cells can also induce changes to ectodermal cells (depending on context) -- tissue types interact with each other & affect their development/differentiation- this is the takeaway.

 

[Blueprint MCAT Tutor]

To you last question, other ectodermal cells / endodermal cells can also induce changes to ectodermal cells (depending on context) -- tissue types interact with each other & affect their development/differentiation- this is the takeaway.

This is a great point about the takeaway here. The MCAT just wants you to know that how cells develop depends on their context. So if a question comes up about it, there's a 99% chance that the answer is, "It will now develop along a new path based on its context".